Metric 60-degree thread
Drill = D - (0.01299 x engagement % x pitch)D and pitch are entered in millimetres. At 75% engagement this is close to the familiar D minus pitch shop rule.
Machining / interactive calculator
Tap Drill Size Calculator
Estimate a starting drill diameter for 60-degree metric and Unified cut threads. Adjust thread engagement and switch units without losing your values.
mm
Major diameter of the internal thread.
mm
Axial distance between adjacent thread crests.
%
A planning value; higher engagement increases tapping torque.
Form taps require the tap manufacturer's recommended hole chart.
Formula & assumptions
How the tap drill estimate is calculated
Unified inch thread
Drill = D - (0.01299 x engagement %) / TPID is in inches. This estimates geometry for a 60-degree cut thread; select a real available drill at or above the calculated value as the process requires.
Production application disclaimerConfirm the drill against the tap manufacturer's chart, thread class, material, coating, hole depth, and required engagement. Do not use this cut-tap estimate for form or roll taps.